// #pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
// #include <x86intrin.h>
using namespace std;
#if __cplusplus >= 202002L
using namespace numbers;
#endif



int main(){
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(ios::badbit | ios::failbit);
	cout << fixed << setprecision(15);
	long long n;
	cin >> n;
	const int m = 1e6;
	vector<long double> h(m + 1);
	for(auto i = 1; i <= m; ++ i){
		h[i] = h[i - 1] + 1.0L / i;
	}
	auto eval = [&](long long x)->long double{
		return x <= m ? h[x] : logl(x) + egamma_v<long double>;
	};
	long double res = 0;
	for(auto x = 1; x <= m; ++ x){
		res += (2 * eval(n / x) - eval(min<long long>(m, n / x))) / x;
	}
	cout << res << "\n";
	return 0;
}

/*

*/